On Friday, February 9, the European Aviation Safety Agency (EASA) issued an Emergency Airworthiness Directive warning operators of a potential dual-engine in-flight shutdown on A320neo family jets powered by Pratt & Whitney’s PW1100G geared turbofan engine. Such a directive is issued when an unsafe condition exists that requires immediate action by an aircraft’s owner or operator.

The directive was issued in the wake of instances of in-flight shutdowns and aborted takeoffs. Pratt & Whitney issued a release Friday stating that the company, with the support of Airbus, is in close contact with customers to address the issue. According to Pratt & Whitney, the problem relates to the knife edge seal in the high-pressure compressor aft hub. The company also stated that the issue is isolated to “a limited subpopulation of engines.”

Airbus has issued an alert providing instructions to de-pair affected engines and discontinue extended-range twin-engine operations (ETOPS). Airbus has since decided to stop accepting further deliveries of PW1100G engines. According to Airbus, the issue can potentially appear on engines starting with serial number P770450. Around one-third of the in-service fleet of A320neo family jets is equipped with the PW1100G, and on 11 aircraft both engines were reported to have the problematic serial number; 21 jets have the serial number on one engine (43 affected engines in total). On Monday, 12 February, Pratt & Whitney said it was evaluating another 55 GTF engines.

One of the customers affected by the issue is Indian low-cost carrier IndiGo, which has grounded three A320neo aircraft. Also, Hawaiian Airlines said in a statement that it has identified an Airbus A321neo that may be impacted, and has removed the aircraft from service.

The issue is the latest in a string of problems that have dogged the GTF program and caused delivery delays for both the Airbus A320neo and Bombardier’s CSeries jet. As a result, buyers have flocked to CFM International and its competing LEAP-1A turbofan.

There are currently 113 GTF-powered A320neo jets flying with 18 customers. Since entering service in January 2016, GTF engines have logged more than 500,000 flight hours.